Java Data Type - 如何舍入数小于等于小数

import java.text.DecimalFormat;

public class Main {

  public static void main(String[] args) {
    double numberToRound = 12345.6789;

    DecimalFormat df = new DecimalFormat("0.000");
    System.out.println("Rounded number = " + df.format(numberToRound));

    System.out.println(String.format("Rounded number = %.3f", numberToRound));

  }
}